NEWARK — U.S. Sen. Robert Menendez accepted a third flight on the private plane of a wealthy campaign donor now under federal investigation that he did not disclose until several years later, something the senator's office called an "oversight."

The powerful Democrat's campaign account has paid more than $400,000 in legal fees connected to investigations surrounding him and Salomon Melgen, a wealthy eye doctor from South Florida, according to a campaign finance report provided by Menendez’s office.

Menendez is now setting up a fund to pay future legal bills.

The disclosures come as the Senate Ethics Committee investigates Menendez’s failure to reimburse Melgen for two 2010 flights on his private plane, valued at a total of $58,500.— Those were round trips to the Dominican Republic, from Florida and New Jersey. Menendez disclosed them on Jan. 30, 2013 — after they drew scrutiny from the media and political opposition.

Paul Brubaker, the state director for Menendez, said the senator accepted an additional flight on Melgen’s private plane on Jan. 30, 2011, from Florida to New Jersey. Menendez had been in Florida for a series of campaign fundraisers.

“Due to an oversight, the campaign did not reimburse Dr. Melgen for the cost of that flight at the time,” Brubaker said. “When that oversight was discovered, at the end of 2013, Sen Menendez directed his campaign to immediately reimburse Dr. Melgen $11,250 for the cost of the flight.”

Menendez is reportedly also being investigated by a federal grand jury as to whether he did favors for Melgen’s business interests.

Menendez’s campaign has paid the Washington law firm McDermott Will & Emery $250,000 for personal representation, and $156,240 to the law firm Perkins Coie to represent the campaign.

Brubaker would not say if the expenses were attributable to a federal investigation or the one undertaken by the ethics committee.

Brubaker said Menendez received permission from the ethics committee to set up the legal fund. It can accept donations of up to donations capped at $10,000 a year. Registered lobbyists, foreign nationals, corporations and labor unions are not permitted to contribute.

The fund will disclose its contributions quarterly with the secretary of the Senate.

Correction: An earlier version of this story said Menendez's campaign had paid more than $360,000 in legal bills. It was more than $400,000.